Piston for gas storage tank



April 14,' 1959 f J. H. WlGGlNS 2 1 PISTON FOR GAS STORAGE TANK Filed June 27, 1956 j 2 Sheets-Sheet 2 INVNTOR.

United States Patent O PISTON FOR GAS STORAGE TANK John I-I. Wiggins, Menlo Park, Calif.

Application June 27, 1956, Serial No. 594,1 94

11-Claims. v (rCl. 48-176) This invention relates to field storage tanks for the storage of gases, and more particularly toimprovements in gas storage tanks of the type in which the gasis stored under pressure under a vertically movable piston contained within the interior of the tank. Tanks of this kind are characterized in that movement of the piston may be utilized to vary the Volume of. the gas receiving space within the tank so as to maintain a variable Volume of gas at substantially constant pressure. Such tanks, broadly speaking, may be used individually for the storage of gas or a number of such tanks may be connected in the field to a plurality of other tanks containing volatile liquids, the connection being made in such a Way that the vapors of the liquids' are received and stored in the gas storage tanks to prevent losses of the vapors due to heat expansion and other causes. Such gas storage tanks, with certain variations in their Construction, may themselves` be used for the storage of volatile liquids. In the latter case, the vapors' of the liquids are collected in the space above the liquid and beneath the piston, the piston being moved by the' gaseous vapor pressure, or by other means, so as to maintain the vapor at a desired pressure.

Tanks of the type referred to above are often quite large in diameter. Since the pistons float upon the stored gas, the pistons must have an overall rigidity sufcient to withstand stresses from the laterally dire'cted peripheral loads to which they are subjected during operation,` and to withstand the stresses set up therein by the gas pressures. The pistons must also have sutficient rigidity to retain their shape when the tanks are out of service and when the pistons are resting upon supports at the bottom of the tanks. Heretofore, such pistons have ordinarily been rigidified by various k 'nds of bridging trusses of fabricated steel, and the overall weight of these steel reinforced pistons has commonly been about 12 to 15 pounds per square foot of piston area, their weight thereby being sufficient to produce a pressure of only about 2 /2 to 3 inches of water in the gas upon which the pistons rest. The cost of steel truss'es and the like is quite high and, while additional steel could be added in order to increase the weight of the piston so as to increase the pressure of the gas therebeneath, the cost of the additional steel quickly becomes prohibitive. Thus', when additional weight has been desired in such pistons, it has heretofore been the practice to provide a number of small concrete blocks Weighing about 200 pounds each, and to distribute these blocks about the top of the piston. Such concrete blocks, however, are relatively expensive in themselves since they may cost as much as $60 to $70 per cubc yard and they are relatively expensive to install. Furthermore, a great number of such blocks is required in order to load a large piston sufliciently to produce a gas pressure as' high, for ex ample, as 6 to 24 inches of water, and their random distribution on a piston produces stresses in the piston that are difficult to compute or predetermine.

One of the objects of the present invention is to pro- 2 vide an improved weightedpiston for a tank for storing gas under pressure, wherein the piston is of relatively simple Construction and far less expensive to build than previously known pistons of comparable strength, size and weight.

Another object of the invention is to provide a piston having the advantages just stated, wherein the piston comprises a thin, relatively flcxible and inexpensive metal diaphragm having. formed in situ thereon a concentrically disposed, rigid monolithic concrete' annulus' which provides not only the desired weight for the piston, but also provides the primary rigidifying and stress absorbing frame for the piston.

Still another object of the invention is to provide a piston of the character just stated wherein the forces tending to flex the piston diaphragm are transmitted to the concrete annulus itself, and the annulus is 'so Situated upon the diaphragm as to serve as a torsion ring in absorbing the flexing, forces exerted upon certain portions of the diaphragm. by the pressure of the gas ther'ebeneath.

Yet another object of the inventionis to provide, in conjunction with the concrete annulus, means by which the laterally directed' peripheral leads to which the piston is subjected are transmitted to the concrete annulus, and means by which the flexin'g forces exerted by the gas upon that portion of the daphragm encompassed by the concrete annulus are transmitted to the annulus so as to produce a torsional moment thereabout in one direction while the corresponding forces exerted by the gas upon the portion of the diaphragm outside the annulus are transmitted to the annulus so as to produce a torsional moment thereabout in the opposite direction, the torsional moments thereby tending to counteract each other and to miuimize the net torsional stresses in the annulus.

Yet another object of the invention is to provide means for supporting the entire piston structure in an elevated position above t-he bottom of' the tank when the tank is not in use, the support means being such that the stresses in the concrete annulus are minimized while the piston is in its supported condition.

These and other objects and advantages of the present invention will be apparent from the following description of a preferred embodiment thereof, taken with the accompanyng drawings, wherein:

Fig'. 1 is a vertical cross-sectional view of" a gas holder or'gas storage tank having emboded the'rein a vertically movable piston constructed in accordance with the present invention, the piston being shown in an elevated condition representing one of the positions which it may occupy while restng or floating upon a body of gas confined within the tank beneath the piston;

Fig. 2 is a fragmentary cross-sectional view showing thepiston supported upon legs which rest upon the bottom of the tank, the piston thus being supported in position for inspection of its under-surface when the tank is not in use; 'H

Fig. 3` is a fragmentary vertical cross-sectional view of the piston showing approxmately one-half of the piston on an enlarged scale;

Fig'. 4 is a one-quarter top plan view of the piston on substantially the same scale employed in Fig. 3; and

Fig. 5 is an enlarged cross-sectional view showing the details by which the piston supporting legs may be Secured to the piston.

In the drawings the numeral 10 designates an upstanding cylindrical wall of a gas storage tank provided with a bottom 11 that may rest directly upon the ground 12 or upon any suitable foundation. The top of the tank is enclosed, in the present instance, by a cone-shaped weather roof 13 which may be supported by any suitable tnss structure 14 having sufficient strength to support the snow loads and the like to which the roof may be subjected. The roof 13 does not itself comprise a part of the present invention, and it need not be constructed so as to be either gas-proof or suitable for withstanding gaseous pressures. The roof, however, is preferably vented, and it may be provided with suitable manholes closed by manhole covers 15 to permit easy access to` the upper interior of the tank.

Gas under pressure is introduced into the lower portion of the tank through a conduit 16, the gas being confined within the tank by the bottom 11 and upright sides and by a vertically movable piston structure which embodies the nove] features of the present invention. The piston structure is adapted during normal use to rest or float upon the body of gas within the tank and to pressurze the gas as a result of the weight of the piston. The piston is freely movable vertically so that the pressure of the gas within the tank will remain substantially constant while its Volume may vary.

The piston comprises a flexible or semi-exible circular diaphragm, designated generally by the numeral 17, preferably fabricated by the welding together of a plurality of relatively light weight, thin metal plates of suitable shape and size. The diameter of the tank and the diamter of the diaphragm 17 therein may be as great as 100 feet or more, depending upon the maximum Volume of gas that is to be stored, and it will be understood that the diaphragm, if employed without rigidifying structure, would be subject to buckling and flexure. In the present invention, however, a rigid concrete annulus 18 of monolithic structure is formed concentrically and in situ upon the upper surface of the diaphragm 17, with the center of the annulus coinciding with the geometric center of the diaphragm. This single annulus provides the principal rigidifying frame for the diaphragm, as will be explained in greater detal below, and its relatively great mass or weight augments the gravitational forces acting upon the diaphragm, thereby producing suhstantial positive pressurization of the body of gas beneath the piston. The annulus is preferahly of a size and diameter such that its circular center line lies fairly close to a circle upon the diaphragm 17 which would evenly divide the total area of the diaphragm. Thus the annulus 18, in efiect, divides the diaphragm into a circular center portion 19 encompassed by the annulus, and an outer portion 20 extending radially outwardly of the annulus.

The annulus 18 is preferably formed upon the diaphragm 17 during the initial stages of the constructon of the tank, during which time the diaphragm 17 will be resting directly upon the bottom 11 of the tank. While the diaphragm is in this condition, a cylindrical inner rim 21 of suitably shaped metal plates is bolted or otherwise erected in an upright condition upon the diaphragm, and a corresponding outer rim 22 is similarly erected to provide a form into which the concrete of the annulus may be directly poured.

The outer periphery of the diaphragm 17 is provided with a circular curb channel member 23 to which there is attached, in a well-known fashion, one edge of a cylindrical, flexible, gas impervious sleeve or curtain 24, the other edge of which is secured in gas-tight fashion to the inner surface of the upright wall 10 of the tank. This curtain 24 serves as a seal to prevent the passage of gas between the outer pen'phery of the diaphragm 17 and the wall 10 of the tank.

4. 'I'he outer portion 20 of the diaphragm is provided with a plurality of radially extending cord members 25 which may be welded to the upper surface of the diaphragm and which, at their respective inner and outer ends, may be welded or otherwise secured to the curb 23 and to the outer rim 22. A plurality of upright channel-shaped posts 26 are welded at their lower ends to the curb 23 and carry a plurality of vertically spaced annular frame mernbers 27 which, with the upright post-s 26, form a frame for an upright fender on the peripheral portion of the diaphragm. In the present embodiment this fender frame is provided with a cylindrical hacking plate 28 that is welded to the annular frame members 27 for the purpose of co Operating with the seal 24, it being appreciated that as the diaphragm is moved vertically within the tank, the seal 24 is progressively folded over at 24a, so that the pressure of the gas beneath the seal causes one portion of the seal to be pressed outwardly against the inner surface of the cylindrical surface of the wall 10 of the tank and causes the other portion of the -seal to be pressed radially inwardly against the cylindrical hacking plate 28.

A plurality of struts 29 extend diagonally upwardly from the outer portion 20 of the diaphragm, the lower outer ends of these struts being welded to the cord members 25 and to the top surface of the diaphragm, if desired, and their upper ends being welded to upright plates 30 that are suitably anchored to the upper portion of the concrete annulus 18, as by radially extending rods 31 or their equivalent embedded in the concrete. A plurality of additional struts 32 extend from the upright fender frame members 26 diagonally downwardly to the plates 30, so that these latter struts brace and reinforce the upstanding tender structure.

The inner portion 19 of the diaphragm is provided with a plurality of circumferentially and radially spaced upright columns 33, 34 and 35 of progresively decreasing height. The tops of the upright columns 33 and 34 are traversed and joined by a plurality of tension rods or cables 36 which have their inner ends welded or otherwise fixed to a circular plate 37 located directly above the axial center `of the diaphragm. The tension members 36 extend from this plate radially outwardly and are tacked to the tops of the columns 33, the upper ends of which may be joined by cross bars 33a. The tension members 36 extend to the tops of the columns 34 where the ends of the tension members are joined to the inner ends of diverging tension members 36a. These latter tension members extend from the columns 34 across the tops of the columns 35 and thence outwardly and downwardly toward the junction of the lower portion of the inner rim 21 with the diaphragm 17 where they are welded or otherwise secured to upright plates 38, which in turn are welded to the upper surface of the diaphragm and are anchored by the diaphragm itself, and by a plurality of rods 38a, to the lower portion of the concrete annulus.

Any suitable means may be employed to balance the present piston assembly while it is in its floating condition upon the body of gas stored in the tank. In the present instance, this balancing is obtained by the use of two well known identical balancing weight systems, only one of which is shown in Fig. l. In the utilization of each of these weight systems to balance the piston assemhly, cables 40 and 41 are secured to the piston assembly at diametrically opposite positions thereon, as at the lower outer ends of the struts 29. The cable 40 extends upwardly through a suitable opening in the roof 13 and across a sheave 42 which may be mounted upon the roof by a suitable frame 43. From the sheave 42 the cable 40 extends across the roof 13 and across a double sheave 44 mounted upon a frame 45, and thence downwardly to a weight 39 hanging outside the tank. The cable 41 extends upwardly from the piston in a similar manner, through an opening in the roof 13 and across a sheave 46 mounted upon the frame 45, and thence across the double sheave 44 and down to the Weight 39. If, for example, the right hand side of the piston, as viewed in Fig. 1, drops below the level of the left hand side, the cable 41 will become slack and the cable 40 will carry the entire load of the weight 39. The application of this load to the right hand side `of the piston by the cable 40 will raise that side until the load of the weight 39 is equally shared hy the two cables 40 and 41, at which time the piston will he level. It will, of course, be understood that while only one weight and cable system -is shown, proper balancng of *thepiston requires at 'least another -like `cab'le system attached *to'the piston-at 90 'degrees from the 'one shown. "Inasmuch 'as this balancing scheme is now well-known, however, illustraton of 'both systems is not believed necessary and further explanat'on of their operation would 'serve no 'useful purpese.

After the piston assembly has been constructed, the piston and the tank are preferably tested for leakage and for proper operation before they are put into service. In this testing, air is pumped into the tank through the 'conduit 16. When suflicient ,air has been introduced into the tank so as to produce a pressure suicient to lift the piston, the piston will begin to rise, the seal`24 preventing escape of the air around the peripheral edges of the daphragm 17. When the piston has been lifted'by the pressure of the air beneath the piston, the inherent balance of the piston may be checked and .if it is found that weight needs to be added here or there in order to obtan sufliciertly perfect balance, additional concrete maybe poured onto 'the annulus 18 at theponts required. In order that this may be done Conveniently, the upper 'edges of the inner and outer rims 21 and 22 may be of suchheight that they normally extend a few inches above the upper surface of the concrete annulus 18. This eX- tra height of the rims will thus aford a form for the additional concrete that may be p-oured upon the annulus for balancng purposes. 'Balancing of the piston may of course 'also be accomplished by placing a few concrete bloc'ks `at proper locations on the top of the annulus.

In connection with the initial test of the tank, or at later times during the life of the tank and the piston, it may be desirable to support the *piston in a position elevated with respect *to the bottom of the tank. For this purpose the piston is provided with means for receiving a number of pipe support legs upon which the piston may rest. A -plurality ofupstanding cylndrical pipe support nozzles 50 are welded upon the upper surface of the diaphragm 17 in the positions shown in the drawings before the-concrete for the annulus 18 is vpoured. These nozzles encompass openings 51 'in 'the diaphragm (see Fig. 1) and extend upwardly'through the concrete annulus to a level `well above its upper surface. As best seen in Fig. 5, the 'uppermost end of each of the pipe support nozzles has a flange 52 welded or otherwise secured thereto so that the 'top faceof the flange is disposed above the uppermost end of 'the support nozzle, the upper edge of each nozzle body thereby providing an internal annular shoulder 53. In its 'normal condition, 'the upper end of each support nozzle is closed by a .cap 54 that is secured to the fiange 52 'by means of 'a plurality of nuts 56 and bolts 57 and a suitable `gasket 55 may be employed beneath each cap.

When it is desired to support the piston upon legs, the piston 'is elevated by introducing air under pressure into the lower portion of the tank through the Conduit 16, the gas 'previously stored in the tank having first been expelled by permitting the piston to sink to the bottom of the tank. `With the piston fioating upon the body of air, the caps `54 are removed from the tops of the upstanding pip'e support nozzles 50 one by one, and a cylndrical pipe-like leg 58 is slipped downwardly inside each pipe support nozzle, the upper edge of each leg having an annular flange 59 formed thereon 'which extends radially outwardly and 'is arranged to be received upon the shoulder 53 of its pipe support nozzle to prevent the leg 58 'from dropping downwardly through the nozzle. After aleg "58 has been received in its corresponding pipe support nozzle 'as shown in Fig. 5, the plate 54 is replaced upon the nozzle to reseal the upper end thereof and to prevent axial movement of the `leg with respect to the nozzle. When the legs have all been installed, 'the air pressure under the piston is relieved and the piston will 'then settle downwardly until the lower ends of the legs come to rest upon 'the bottom 1-1 of .the tank as shown in Fig. 2, in which condition the piston will "be supported in a sufciently elevated position with respect 'to 'the bottom 11 of 'the tank to *pernt access to the space beneath the piston for cleaning purposes or for maintenance 'and inspection.

The pressure under which gas is stored in "the present tank will of course depend upon the total eifective weight of 'the piston assembly and its concrete annulus 18. The weight of the diagphragm 17 and the other steel ele- 'ments of the piston assembly can easily be computed 'for a piston of a given diameter and Construction and, since the weight of concrete of 'a given mixture is known, the amount of concrete needed in the 'annulus to produce a desired gas pressurecan likewise be computed. Due to the mass of the concrete in the annulus, pistons constructed in accordance With the present'invention may be inexpensively built to provide `any'reasonable y gas storage pressure desired. For example, storage 'pressures of from 6 to 24 inches of water, and higher pressures, can easily be provided merely by varying the amount of concrete in the annulus. At these pressures (roughly, 2 to 9 pounds per square inch) the legs 58 can be installed in the piston or removed therefrom without the loss of any appreciable gas Volume as compared to the 'total Volume of the gas confined beneath the piston.

It will be observed that when the piston is resting upon 'the body of gas therebeneath in the floating condition shown in Fig. l, the upwardly directed pressure forces exerted by the gas upon the outer peripheral portion 20 of the diaphragm seeks to flex that portion of 'the diaphragm upwardly. These forces, however, are transmitted to the upper portion of the annulus 18 by the diag- 'onally upwardly extending struts 29 which are in a state of compression during flotation 'of the piston. Since the upper ends of the struts 29 are anchored to the upper portion of the concrete annulus 18 above its cross-sectional center of gravity 60 (Fig. 3), the forces of the gas exerted upon the peripheral portion 20 of the diaphragrn will produce a torsional moment about the concrete annulus 18 in the direction of the arrow 61. At the same time, however, the upwardly directed forces of the pressurized gas exerted upon the central portion 19 of 'the diaphragm will produce compressive forces in the columns 33, 34, and 35 which is transmitted to the members 36 and 36a, producing a state of tension therein. The tensle force in the members 36 and 3611 thus produced by the upwardly directed forces of the gas pressure on the central portion '19 of the diaphragm, is transmitted to the upstanding plates 38 and thence to the lower portion of the concrete annulus, thereby producing a torsional moment about the annulus in the direction indicated by the arrow 62 in Fig. 3. Thus, the torsional moments produced about the concrete annulus by the pressure of the gas upon the portions 19 and 20 of the diaphragm are in opposite directions and tend to neutralize -each other and thereby minimize the net torsional stresses existing in the annulus 18 while the piston is in its float- 'ing state. By calculation, the diameter and disposition of the concrete annulus can be arranged so that these moments are equal to each other.

It will be observed, furthermore, that the pressure of the gas acting upon the portion of the seal 24 that is backed up by the upstanding cylndrical plate 28 ,eXerts a radially inwardly directed force upon the upstanding fender assembly on the periphery of the piston. This force is transmitted directly to the concrete annulus 18 by the radially downwardly directed struts 32 as well as by the struts 29 and by the metal of the plates comprising the peripheral portion 20 of the diaphragm. It will .also be understood that other well-known types of seals, other than the curtain seal 24, may be employed in conjunction with the present invention. For example, `grease seals or tar seals of any well-known type may be used, in which event the upstanding fenderassembly on the periphery of the diaphragm *will carry rollers that Will .concrete annulus 18 has been formed therebetween.

ride in a well-known fashion upon the inner surface of the tank wall 10 to guide the piston. When seals of this latter type are used, the lateral radially inwardly directed forces to which the upstanding fender will be subjected by the rollers carried thereon will likewise be transmitted directly to the concrete annulus 18 by the struts 32 and the other related structure.

If desired, the inner and outer rims 21 and 22 may be constructed so that they may be removed after the In that event there will be no permanent connection made between the rims and other parts of the piston assembly and it may be desirable to anchor the annulus 18 to the upper surface of the diaphragm by means of upstanding lugs welded upon the upper surface of the diaphragm and embedded in the lower portion of the annulus. In any event, it will be observed that the simple and inexpensively formed concrete annulus 18 serves not only as the principal load member of the piston, but also as its principal or primary rigidifying element. During operation of the tank and piston, lateral forces exerted upon the piston by the gas pressure upon that portion of the seal 24 backed by the cylindrical plate 28, or by the guide rollers that will be employed on the upstanding peripheral fender when other types of seals are used, are transmitted directly to the annulus 18. The diaphragm flexing forces exerted upon the piston by the gas therebeneath are likewise transmitted to the annulus in the manner discussed above, with the annulus absorbing these forces in torsional moments thereabout which tend to neutralize each other. Because one torsional moment tends to counteract the other within the concrete annulus,

internal reinforcement within the concrete is not necessary for the absorption of these forces and the cost of the Construction is thus further reduced.

During those periods during which the piston is supported upon the legs 58, it will be noted that the concrete annulus 18 again serves as the principal rigidifying element for the piston assembly. At this time the weight of the peripheral portion 20 of the diaphragm and the upstanding fender thereon is transmitted to the annulus priman'ly by the diagonally disposed struts 29, and the weight of the inner portion of the diaphragm is applied to the annulus either by the inner and outer rims 21 and 22 or, When the rims are removable, by the previously mentioned lugs by which the annulus may be anchored to the diaphragm. Furthermore, since the weight of the annulus and the weight of the remaining portions of the piston are carried by the legs 58 which are located within and directly beneath the concrete annulus, the position of the legs and the leg receiving nozzles 50 may be arranged radially with respect to the piston so that no excessive stresses exist in the concrete while the piston is at rest on the legs. If desired, however, circular reinforcing members 63 may be embedded in the upper portion of the annulus, as shown in Fig. 3, so as to minimize the tensional forces to which certain portions of the concrete in that area may be subjected during periods in which the piston is at rest upon the legs 58.

The foregoing description of one embodiment of the present invention has been given for clearness of understanding only and not for purposes of limitation, for it will readily be appreciated by those skilled in the art that numerous variations may be made in the embodiment shown without departing from the spirit and scope of the claims appended hereto.

I claim:

1. In an upstanding substantially cylindrical tank tor storing gas under pressure, the vertically movable piston combination comprsing a substantially circular semifiexible metal diaphragm disposed within the tank and adapted to rest by gravity upon the body of gas contained therein and arranged for free vertical movements within the tank upon increase and decrease of the Volume of the body of gas, scaling means about the periphery of said diaphragm cooperating with the upright cylindrical side wall of the tank to prevent leakage of the gas between the periphery of said diaphragm and the wall of the tank, a rigid upstanding concrete annulus of substantial weight supported concentrically upon the upper side of said diaphragm to increase the gravitational forces acting upon said diaphragm and thereby increase the pressure of the gas, said annulus dividing said diaphragm into a central portion encompassed by said annulus and an annular peripheral portion extending radially outwardly from said annulus, means for transmitting to said annulus the upwardly flexing forces exerted upon said peripheral portion of said diaphragm by the gas disposed therebelow so as to produce a first torsional moment in a first direction about said annulus, and means for transmitting to said annulus the upwardly flexing forces exerted upon said central portion of said diaphragm by the gas disposed therebelow so as to produce a second torsional moment in a second direction about said annulus, said first and second directions being opposite to each other and said first and second torsional moments being substantially equal, whereby said torsional moments tend to balance and to counteract each other so as to minimize the net resulting torsional stresses in said annulus.

2. The combination set forth in claim 1, wherein said concrete annulus is of one piece constructon.

3. The combination set forth in claim 1, wherein said concrete annulus is disposed in an upstanding annular retaining form arranged concentrically upon the upper side of said diaphragm.

4. In an upstanding substantially cylindrical tank for storing gas under pressure, the vertically movable piston combination comprising a substantially circular semiflexible metal diaphragm disposed within the tank and adapted to rest by gravity upon the body of gas contaired therein and arranged for free vertical movements within the tank upon increase and decrease of the Volume of the body of gas, an upstanding cylindrical fender on the peripheral extremity of said diaphragm, scaling means about the periphery of said diaphragm cooperating with the upright cylindrical side wall of the tank and with said fender to prevent leakage of the gas between the periphery of said diaphragm and the wall of the tank, a rigid upstanding concrete annulus of substantial weight supported concentrically upon the upper side of said diaphragm to increase the gravitational forces acting upon said diaphragm and thereby increase the pressure of the gas, said annulus being disposed well radially inwardly from said fender and divding said diaphragm into a central portion encompassed by said annulus and an annular peripheral portion extendng well radially outwardly from said annulus, said fender being subjected to radially inwardly directed forces during the vertical movements of said diaphragm, means for transmitting directly from said fender to said annulus a substantial portion of said radially inwardly directed forces to which said fender is subjected, a plurality of circumferentially spaced struts extending diagonally upwardly and radially inwardly from said peripheral portion of said diaphragm to the upper portion of said annulus, whereby pressure forces exerted by the gas upon the underside of said peripheral portion of said diaphragm and tending to flex said peripheral portion of said diaphragm upwardly are transmitted to said annulus and produce a torsional moment thereabout in a first direction, and means for transmitting to the lower portion of said annulus the corresponding pressure forces exerted by the gas upon said central portion of said diaphragm so as to produce another torsional moment about said annulus in the opposite direction, said torsional moments thereby tending to balance and to counteract 'each other so as to minimize the net resulting torsional stresses in said annulus.

5. In an upstanding substantially cylindrical tank for storing gas under pressure, the vertically movable piston 'combination ..comprising a 'substantially circular semiflex'ible metal ,diaphragm disposed within 'the tank and 'adapted to rest `by 'gravity upon "the body .of gas con- *ta'ined therein 'and arranged for free vertical movements within the tank upon increase and ;decrease of the volume of "the body *of gas, 'sealingmeans about the periphery `*of said diaphragm cooperating with the uprght cylindrical side wall 'of the *tank to prevent leakage of the gas 'between'the perphery of'said diaphragm and the wall -of `'the tank, a rigid upstanding concrete 'annulus 'o'f substantial weight supported concentrically upon the uppens'ide 'of saiddiaphragmand dividing said diaphragm into a central portion encompassed 'by said annulus and an annular perpheral ;portion extending ,radially outwardly from said annulus, said annulus providing the principal rigidifiying frame 'for said diaphragm and the weightof said annulusserving materially to increase the gravitational forces acting upon `said tdiaphragmso 'as to increase the pressure of the gas, and .means `for :transmittng 'to said annulus a major portion of the forces exerted upon said central portion of said diaphragm and upon said peripheral portion of said diaphragm that tend to flex said portions ofsaid .diaphragm vertically with respect to saidrannulus.

6. In an *upstanding substantially cylindrical tank for storing gas under pressure, the vertically movable piston combination comprising a substantially circular semiflexible metal diaphragm disposed within the tank and adapted to rest by gravity upon the body of gas contained therein and arranged for free vertical movements within the tank upon increase and decrease of the Volume of the body of gas, sealing means about the perphery of said diaphragm cooperating with the uprght cylindrical side wall of the tank to prevent leakage of the gas between the perphery of said diaphragm and the wall of the tank, a rigid upstanding concrete annulus of substantial weight supported concentrically upon the upper side of said diaphragm to increase the gravitational forces acting upon said diaphragm and thereby increase the pressure of the gas, said annulus providing a rigidifyng frame for said diaphragm and having a maximum diameter substantially less than that of said diaphragm so that the perpheral portion of said diaphragm extends radially outwardly from said annulus, and means for transmitting from said peripheral portion of said diaphragm to said annulus a major portion of the forces exerted by the gas upon said peripheral portion of said diaphragm.

7. In an upstanding substantially cylindrical tank for storing gas under pressure, the vertically movable piston combination comprising a substantially circular semiflexible metal diaphragm disposed within the tank and adapted to rest by gravity upon the body of gas contained theren and arranged for free vertical movements within the tank upon increase and decrease of the volume of the body of gas, an upstanding cylindrical fender on the perpheral extremity of said diaphragm, scaling means about 'the perphery of said diaphragm cooperating with the uprght cylindrical side Wall of the tank and with said fender to prevent leakage of the gas between the perphery of said diaphragm and the wall of the tank, a rigid upstanding concrete annulus of substantial weight'supported concentrically upon the upper side of said diaphragm to increase the gravitational forces acting upon said diaphragm and thereby increase the pressure of the gas, said annulus providing a rigdifying frame for said diaphragm and having a maximum diameter substantially less than that of said diaphragm so that said annulus is disposed well radially inwardly from said fender and so that the peripheral portion of said diaphragm extends well radially outwardly from said annulus, said fender being subjected to radially inwardly directed forces during the vertical movements of said diaphragm, and means including compression struts extending from said fender and from said peripheral por- 10 'tion of said diaphragm to said annulus for transmitting' directly to said annulus a major portion of said radially inwardly directed forces to which `said fender is subjected and a major portion o'f the forces exerted by thegas upon said peripheral portion of said diaphragm.

8. In an upstanding substantially cylindrical 'tank 'for storing gas under pressure, the vertically movable piston combination comprising a substantially circular semifiexible metal diaphragm disposed within the tank and adapted to rest by gravity upon the body of gas contained theren and arranged for 'free vertical movements within the tank upon increase and decrease of the Volume of the body of gas, sealing means about the perphery of said diaphragm cooperating with the uprght cylindrical side wall of the tank to prevent leakage of the gas between 'the perphery of said diaphragm and the wa'll of .the 'tank, a rigid upstanding concrete annulus of substantia'l weight .supported concentrically upon the upper side of said diaphragm and dividing said diaphragmnto a central portion encompassed by said annulus and :an annular peripheral portion extending radially outwardly from 'said annulus, said annulus providing the principal rigidifying frame for ;said diaphragm and the weight of said annulus 'serving materially to increase .the gravitational forces acting upon said diaphragm so as to increase the pressure of the gas, means for transmitting from said peripheral portion of said diaphragm to said annulus a major portion of the forces exerted by the gas upon said peripheral portion of said diaphragm so as to produce a torsional moment about said annulus in one direction, and means for transmitting to said annulus the corresponding pressure forces exerted by said gas upon said central portion of said diaphragm so as to produce another torsional moment about said annulus in the opposte direction, said torsional moments thereby tending to balance and to counteract each other so as to minimize the net resulting torsional stresses in said annulus.

9. The combination set forth in claim 8, wherein said last-mentioned means includes upstanding struts on said central portion of said diaphragm interconnected by flexible tension members anchored to said annulus.

10. In an upstanding substantially cylindrical tank for storing gas under pressure, the vertically movable piston combination comprising a substantially circular semiflexible metal diaphragm disposed within the tank and adapted to rest by gravity upon the body of gas contained therein and arranged for free vertical movements within the tank upon increase and decrease of the Volume of the body of gas, an upstanding cylindrical fender on the perpheral extremity of said diaphragm, scaling means about the perphery of said diaphragm cooperating with the uprght cylindrical side wall of the tank and with said fender to prevent leakage of the gas between the perphery of said diaphragm and the wall of the tank, a rigid upstanding concrete annulus of substantial weight supported concentrically upon the upper side of said diaphragm and disposed well radially inwardly from said fender and dividng said diaphragm into a central portion encompassed by said annulus and an annular perpheral portion extending well radially outwardly from said annulus, said annulus providing the principal rigidifying frame for said diaphragm and the weight of said annulus serving materially to increase the gravitational forces acting upon said diaphragm so as to increase the pressure of the gas, said fender being subjected to radially inwardly directed forces during the vertical movements of said diaphragm, means for transmitting directly from said fender to said annulus a substantial portion of said radially inwardly directed forces to which said fender is subjected, and means for transmitting to said annulus a major portion of the forces exerted upon said central portion of said diaphragm and upon said peripheral portion of said diaphragm that tend to flex said portions of said di`aphragm vertically with respect to said annulus.

11. In au upstanding substantially cylindrical tank for 1-1 storing gas under pressure, the vertically movable piston combination comprising a snbstantially circular semi-flexible metal diaphragm disposed within the tank and adapted to rest by gravity upon the body of gas contained therein and arranged for free vertical movements within the tank upon increase and decrease of the Volume of the body of gas, an upstanding cylindrical fender on the peripheral extremity of said diaphragm, sealing means about the periphery of said diaphragm cooperating with the uprght cylindrical side wall of the tank and with said fender to prevent leakage of the gas between the periphery of said diaphragm and the wall of the tank, a rigid upstanding concrete annulus of substantial weight supported concentrically upon the upper side of said diaphragm and disposed well radially inwardly from said fender and dividing said diaphragm into a central portion encompassed by said annulus and an annular peripheral portion extending well radially outwardly from said annulus, said annulus providing the principal rigidifying frame -for said diaphragm and the weight of said an- 20 nulus serving materially to increase the gravitational forces acting upon said daphragm so as to increase the pressure of the gas, said fender being subjected to radially 'nwardly directed forces during the vertical movements of said diaphragm, means for transmitting directly from said fender to said annulus a substantial portion of said radially inwardly directed forces to which said fender is subjected, a plurality of vertcally extending legs 10- cated only beneath said annulus for supporting said diaphragm upon the bottom of the tank when said diaphragm is not resting upon the body of gas, and means for transmittng to said annulus, both when said diaphragm is resting upon the gas and when said diaphragm is supported upon said legs, a major portion of the forces exerted upon said central portion of said diaphragm and upon said peripheral portion of said diaphragm that tend to flex said portions of said daphragm vertically with respect to said annulus.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,417 Prager et al. Oct. 16, 1951 2,071,530 Howard et al. Feb. 23, 1937 2,089,645 Dickmann Aug. 10, 1937 2,663,453 Wiggins et al Dec. 22, 1953 2,750,067 Wiggins June 12, 1956 FOREIGN PATENTS 40,779 Germany Sept. 15, 1887 

1. IN AN UPSTANDING SUBSTANTIALLY CYLINDRICAL TANK FOR STORING GAS UNDER PRESSURE, THE VERTICALLY MOVABLE PISTON COMBINATION COMPRISING A SUBSTANTIALLY CIRCULAR SEMIFLEXIBLE METAL DIAPHRAGM SIDPOSED WITHIN THE TANK AND ADAPTED TO REST BY GRAVITY UPON THE BODY OF GAS CONTAINED THEREIN AND ARRANGED FOR FREE VERTICAL MOVEMENTS WITHIN THE TANK UPON INCREASE AND DECREASE OF THE VOLUME OF THE BODY OF GAS, SEALING MEANS ABOUT THE PERIPHERY OF SAID DIAPHRAGM COOPERATING WITH THE UPRIGHT CYLINDRICAL SIDE WALL OF THE TANK TO PREVENT LEAKAGE OF THE GAS BETWEEN THE PERIPHERY OF SAID DIAPHRAGM AND THE WALL OF THE TANK, A RIGID UPSTANDING CONCRETE ANNULUS OF SUBSTANTIAL, WEIGHT SUPPORTED CONCENTRICALLY UPON THE UPPER SIDE OF SAID DIAPHRAGM TO INCREASE THE GRAVITATIONAL FORCES ACTING UPON SAID DIAPHRAGM AND THEREBY INCREASE THE PRESSURE OF THE GAS, SAID ANNULUS DIVIDING SAID DIAPHRAGM INTO CENTRAL PORTION ENCOMPASSED BY SAID ANNULUS AND AN ANNULAR PERIPHERAL PORTION EXTENDING RADIALLY OUTWARDLY FROM SAID ANNULUS, MEANS FOR TRANSMITTING TO SAID ANNULUS THE UPWARDLY FLEXING FORCES EXERTED UPON SAID PERIPHERAL PORTION OF SAID DIAPHRAGM BY THE GAS DISPOSED THEREBELOW SO AS TO PRODUCE A FIRST TORSIONAL MOMENT IN A FIRST DIRECTION ABOUT SAID ANNULUS, AND MEANS FOR TRANSMITTING TO SAID ANNULUS THE UPWARDLY FLEXING FORCES EXERTED UPON SAID CENTRAL PORTION OF SAID DIAPHRAGM BY THE GAS DISPOSED THEREBELOW SO AS TO PRODUCE A SECOND TORSIONAL MOMENT IN A SECOND DIRECTION ABOUT SAID ANNULUS, SAID FIRST AND SECOND DIRECTIONS BEING OPPOSITE TO EACH OTHER AND SAID FIRST AND SECOND TORSIONAL MOMENTS BEING SUBSTANTIALLY EQUAL, WHERBY SAID TORSIONAL MOMENTS TEND TO BALANCE AND TO COUNTERACT EACH OTHER SO AS TO MINIMIZE THE NET RESULTING TORSIONAL STRESSES IN SAID ANNULUS. 